Mixing and kneading apparatus

ABSTRACT

In the case of a mixing and kneading apparatus for the, in particular, thermal treatment of products in the liquid, pasty and/or pulverulent state, with or without the supply and discharge of gases and vapors, in a housing (1), a shaft (2) rotating in said housing and having disk segments (3) or similar disc-like elements arranged on it, which segments or elements interact with mating kneading elements (7) fixed on the housing, the intention is to form, between the mating kneading elements (7), and between the mating kneading elements and the disk segments, an open space (12) in which a mixing arm (14) engages from the shaft (2). In this case, mixing arms (14) of different configurations engage in the open space (toric space 12) from the shaft (2).

The invention relates to a mixing and kneading apparatus for the, inparticular, thermal treatment of products in the liquid, pasty and/orpulverulent state, with or without the supply and discharge of gases andvapors, in a housing, a shaft rotating in said housing and having disksegments or similar disc-like elements arranged on it, which segments orelements interact with mating kneading elements fixed on the housing,there being formed between the mating kneading elements, and between themating kneading elements and the disk segments, an open space in which amixing arm engages from the shaft.

Such mixing and kneading apparatuses are known, for example, from GermanPatent Specification 23 49 106 or from U.S. Pat. No. 3,678,422. Thearrangement shown therein ensures a very good mixing and kneadingaction. Furthermore, encrustations of product on, in particular, heatedelements of the apparatus, for example shaft, housing wall, disksegments and the like, are avoided effectively. However, in the case ofcertain products, in particular in the case of viscous pasty products, atorus of product forms in those regions between two disk segments inwhich there is no product treatment by a mating kneading element and, inthe worst-case scenario, it is possible for this torus of product toremain in these regions, in which case it is not kneaded any further. Inorder to avoid this, it is expedient to use a mixer arm which isfastened on the shaft and engages in the toric space. As a result, theformation of a dead space in which the product does not undergo anytreatment is avoided.

The object of the present invention is to make additional improvementsto the mixing and kneading action in the toric space.

This object is achieved in that mixing arms of different configurationsengage in the open space (toric space) from the shaft.

The different configurations of the mixing arms should be such that theentire toric space is worked by means of relatively narrow mixing arms.That is to say non-worked spaces within the toric space are avoided, asa result of which the mixing and kneading action is considerablyimproved. The distribution of the product is more uniform as a resultsince there are more elements which move the product. This also improvesthe mixing action. Furthermore, the situation where mixing arms onlyever move on one pre-determined path, in which case the shaft issubjected to considerable force-absorbing peaks if, for example, a toruscollapses, is avoided. The different configurations of the mixing armsmean that the product is distributed uniformly in the machine, withresult that the absorption of force by the shaft is balanced out.

Each mixing arm preferably comprises a stem and a crossbar. In oneexemplary embodiment of the invention, the idea is that the crossbarshould always be of the same configuration, while the stem has adifferent length.

In contrast, in the case of another exemplary embodiment, it is alsopossible for the stem to have the same length, and to projectapproximately into the center of the toric space, but for the crossbarof mixing arms within an annular toric space to be of differentconfigurations. Said crossbar may be set obliquely, turned round,curved, twisted, Z-shaped or S-shaped or the like. There are a largenumber of configurations which are intended to be covered by theinvention.

In order that the mixing arm can move through the product better, itshould be configured like a plowshare in cross section. There are anumber of variations in this case too, and these depend on the productwhich is to be worked.

Further advantages, features and details of the invention can begathered from the following description of preferred exemplaryembodiments and with reference to the drawing in which:

FIG. 1 shows a longitudinal section through part of a kneading andmixing apparatus according to the invention;

FIG. 2 shows a cross section through the kneading and mixing apparatusaccording to FIG. 1;

FIGS. 3 to 6 show plan views of different exemplary embodiments ofmixing arms in a toric space formed by two mating kneading elements; and

FIGS. 7 to 9 show cross sections through different exemplary embodimentsof mixing arms.

FIG. 1 shows a drum-like housing 1 of a mixing and kneading apparatus, ashaft 2 rotating in said housing. Spaced-apart disk segments 3 arearranged on the said shaft 2 and bear a kneading bar 5 in the vicinityof an inner wall 4 of the housing 1.

When the shaft 2 rotates in the direction z (see FIG. 2), the kneadingbars 5 pass through kneading gaps 6 which are formed, in conjunctionwith the inner wall 4, by mating kneading elements 7. In the presentexemplary embodiment, the mating kneading elements 7 are of C-shapeddesign. They are fixed on the housing 1 via a foot 8. Adjoining the foot8, a kneading arm 9 runs approximately parallel to the inner wall 4, inthe direction of the longitudinal axis A of the housing 1. Together withthe inner wall 4, this kneading arm 9 forms the kneading gap 6. Thekneading arm 9 is adjoined by a scraping arm 10, which runsapproximately radially with respect to the shaft 2, in the vicinity ofthe disk segment 3. In the vicinity of the shaft 2, said scraping arm 10merges into a shaft arm 11 which, in turn, runs approximately parallelto the shaft 2 and in axis-parallel manner with respect to thelongitudinal axis A, in the opposite direction to the kneading arm 9.The scraping arm 10 and shaft arm 11 essentially have the task ofpreventing encrustations of product on the disk segments 3 and the shaft2, since these two elements of a kneading and mixing apparatus areusually heated. The kneading bar 5 also has this task in relation to theinner wall 4, the kneading bar 5 additionally performing the task ofkneading the product in the kneading gaps 6.

There are usually a plurality of mating kneading elements 7, but atleast two of such elements, distributed in an annular space formed bytwo disk segments 3. In this case, the mating kneading elements 7alternate in direction, as is illustrated by dashed lines in FIG. 1.Together, however, they form a toric space 12, which is largely filledwith the product which is to be treated.

However, in order that the product is likewise mixed and kneaded in asuitable manner in this toric space 12, mixer arms 14 project into saidtoric space 12. In FIG. 1 the mixing arms are designed as T-fingers,each comprising a stem 15 and a crossbar 16.

In the case of the exemplary embodiment according to FIGS. 1 and 2, theinvention provides that the crossbar 16 is always of the same design,but the stem 15.1, 15.2 and 15.3 for different mixing arms 14.1, 14.2and 14.3 within an annular toric space 12 has a different length l₁, l₂and l₃. This makes it possible to work the entire toric space 12 duringa revolution of the shaft 2, with result that, within the toric space12, there are no dead zones in which the product could possibly remain.This means that the product is always kept on the move, encrustations ofproduct are reduced and the kneading action is considerably improved.Furthermore, there is a reduction in force-absorbing peaks duringrotation of the shaft 2, since the product is always worked by at leasttwo mixing arms 14. It is not possible for the following mixing arm tomove through the product in the same track as that produced by thepreceding mixing arm.

Such an arrangement of relatively narrow elements which project into thetoric space to different extents is particularly expedient in mixing andkneading apparatuses whose internal dimensions are at a specific ratiowith respect to one another. The important parameter for this purpose isthe distance a of the shaft 2 from the inner wall 4 of the housing 1,this being formed from half of a diameter d of the shaft 2 and of aninternal diameter D of the housing 1. This distance a should be greaterthan 5S, where S may be the width of the foot 8, of the stem 15, of thecrossbar 16, of the kneading bar 5 or the like. It is only when thedistance a is above 5S that the arrangement of different mixing arms isusually appropriate.

FIGS. 1 and 2 only show one exemplary embodiment of such differentmixing arms. Further exemplary embodiments are shown in FIGS. 3 to 6,although the invention is not intended to be restricted to theseexemplary embodiments either. For the sake of simplicity, FIGS. 3 to 6show a toric space 12 as always being formed by two mating kneadingelements 7.1 and 7.2 which are arranged opposite one another, althoughin practice these elements are merely offset with respect to oneanother.

According to FIGS. 3 to 5, the stem 15.4, 15.5 and 15.6 always has thesame length, with the result that it terminates approximately in thecenter of the toric space 12. It is indicated in FIG. 3 that thecrossbar 16.1 need not run, as is illustrated in FIG. 1, in anaxis-parallel manner, but rather may be arranged in an inclined mannerwith respect to the longitudinal axis A. Within an annular toric space,it is then possible for different crossbars shown to alternate withcrossbars which also run in an axis-parallel manner.

However, it is also possible, as is shown in FIGS. 4 and 5, for thecrossbars 16.2, 16.3 to be bent in a wave-shaped or S-shaped manner.C-shaped crossbars or those which run in a zigzag fashion are alsoconceivable. The shape of the crossbars depends in each case on theproduct which is to be treated.

In FIG. 6, the toric space 12 is only indicated by dashed lines. Afinger-like mixing arm 14.7 engages in it, and the transverse finger 17of said mixing arm alternates its orientation to the left and right, andthe stem 15.7 of said mixing arm has a different length.

As far as treating all the product in the toric space 12 is concerned,the cross section of the elements which move through the product alsoseems to be important. These elements include, in particular, the mixingarm 14, but also the kneading bar 5, an edge of the disk segment 3, andthe mating kneading element 7. The cross section is preferably designedlike a plowshare, it being possible for this to have a straightforwardtriangular cross section according to FIG. 8.

However, in order better to form a discharge surface, the cross sectionis of a desk-like design according to FIG. 7, it being possible for oneside also to be grooved, as indicated by dashed lines. This improvesdischarge of the product.

In the case of products which have a pronounced tendency to form crusts,a cross section according to FIG. 9 is preferred, this cross sectionresulting in a high displacement capacity and thus in good productmovement.

We claim:
 1. Mixing and kneading apparatus, which comprises: a housing;a shaft rotating in said housing and having similar disc-like elementsarranged on said shaft; mating kneading elements fixed on said housing;wherein said disc-like elements interact with said mating kneadingelements; an open toric space formed between the mating kneadingelements and between the mating kneading elements and the disc-likeelements; a plurality of mixing arms extending from the shaft whichengage said open space; wherein the mixing arms following one after theother around the shaft are configured such that they work essentiallythe entire axial cross section of the open toric space.
 2. Mixing andkneading apparatus according to claim 1, wherein said disc-like elementsare disc segments.
 3. Mixing and kneading apparatus according to claim1, wherein said open space is an annular space.
 4. Mixing and kneadingapparatus according to claim 1, wherein said mixing arms include a stemand a crossbar.
 5. Mixing and kneading apparatus according to claim 4,wherein within said open space at least some stems have differentlengths than other stems.
 6. Mixing and kneading apparatus according toclaim 4, wherein within said open space at least some crossbars havedifferent lengths than other crossbars.
 7. Mixing and kneading apparatusaccording to claim 4, wherein the crossbars of the mixing arms withinsaid open space are at least one of set obliquely, curved and twisted inrelation to a longitudinal axis of the housing.
 8. Mixing and kneadingapparatus according to claim 4, wherein at least one of the stem and thecrossbar are designed like a plowshare in cross section.
 9. Mixing andkneading apparatus according to claim 4, wherein the housing has aninner wall and the kneading elements have a width, wherein the distanceof the shaft from the inner wall of the housing is greater than fivetimes the width of the kneading elements.
 10. Mixing and kneadingapparatus according to claim 4, wherein mating kneading elements arearranged opposite each other.
 11. Mixing and kneading apparatusaccording to claim 4, wherein the stem terminates approximately in thecenter of the open space.